.alpha.-Olefins have been polymerized in contact with a catalytic system composed of solid TiCl.sub.3 or of a solid composition of TiCl.sub.3 with a metallic halide and an activator composed of an organic compound of aluminum.
Such solid TiCl.sub.3 and solid composition are prepared by different known processes.
One of these processes consists of reducing TiCl.sub.4 by means of hydrogen. When the resulting reduced chloride is used in the polymerization of .alpha.-olefins, however, reaction rate is low and the obtained product contains large amounts of amorphous polymer.
Another process consists of effecting the reduction of TiCl.sub.4 by means of metallic aluminum. The reaction product contains TiCl.sub.3 and AlCl.sub.3. As these two chlorides are isomorphous, they cocrystallize and cannot be separated by conventional methods. When these compositions are used for the polymerization of .alpha.-olefins, large amounts of amorphous polymer likewise result.
According to another method of manufacturing TiCl.sub.3, TiCl.sub.4 is reduced by means of an alkylaluminum. The resulting TiCl.sub.3 is normally brown and must be converted into violet TiCl.sub.3 in order to obtain stereospecific polymerization of .alpha.-olefins therewith. Even after this conversion the stereospecificity of the catalyst usually remains mediocre.
To improve the stereospecificity of such catalystic system, complexing agents are used to reduce the amount of aluminum derivatives present in the reduced solid.
Thus, in Dutch Patent Application No. 66.10335 of July 22, 1966, in the name of Soc. Italiana Resine, a process for the preparation of TiCl.sub.3 is described in which the reduction of TiCl.sub.4 is effected by an organometallic compound and an ether is a constituent of the reaction medium. The temperature of the reaction medium is brought to between 150.degree. and 200.degree. C. to promote the stereospecificity of the catalytic system.
British Patent No. 1,139,450 of Dec. 27, 1967, in the name of Shell, describes a process for preparing beta TiCl.sub.3 in which TiCl.sub.4 is reduced by diethylaluminum chloride. The ethylaluminum dichloride formed in the course of this reaction is removed by bringing it into contact with a complexing agent. The beta crystalline form is converted into the gamma form so that a more stereospecific catalytic system can be obtained by heat treatment, preferably effected at a temperature between 150.degree. and 160.degree. C.
Belgian Patent No. 610,761 of Nov. 24, 1961, in the name of Eastman Kodak describes a process for preparing TiCl.sub.3 in which the reduction of TiCl.sub.4 is effected by aluminum and in the presence of a complexing agent capable of forming a complex with the aluminum halide formed in the course of the reaction. The complex is soluble in the complexing agent.
Belgian Patent No. 655,308 of Nov. 5, 1964, in the name of Mitsui, describes a process for preparing a catalytic composition in which a composition containing violet TiCl.sub.3 is ground in the presence of a small amount of a monoether or monoketone. The composition is obtained by reducing TiCl.sub.4 with metallic aluminum powder in the presence of AlCl.sub.3. With these catalytic compositions there are obtained polymers, the content of amorphous products of which is relatively low.
The use of ether in the preparation of the catalytic complex improves the stereospecificity and slightly improves the activity of the catalytic system used; the latter, however, remains fairly low.